1. Field of the Invention
This invention relates to an image forming apparatus, such as an electrophotographic printer, for forming an image onto an image bearing member and, more particularly, to an image forming apparatus including an image transfer member for transferring an image onto a recording medium and including a cleaning member for cleaning the image transfer member.
2. Description of the Related Art
Generally, in conventional image forming apparatuses, a surface of an image bearing member, such as a photosensitive drum, is charged by a main charger. Exposing the surface of the drum with a light source creates a latent image on the charged photosensitive drum. A developing unit then develops the latent image using a development agent (toner) to create a visible image. Subsequently, the developed visible image is then transferred by an image transfer unit onto a recording medium such as a paper sheet.
Recently, many image transfer units utilize a transfer roller which contacts the photosensitive drum for transferring the image, formed on the drum, onto the paper sheet. For example, U.S. Pat. No. 5,010,370 discloses an image transfer unit having a transfer roller which is formed of a conductive and elastic outer layer (e.g., rubber). Also, Japanese Patent Disclosure (Kokai) No. 60-229079 discloses an image transfer unit having a transfer roller including at its periphery a conductive and elastic brush consisting of a plurality of bristles (e.g., carbon and nylon). Image transfer units utilizing transfer rollers are more desirable than transfer units utilizing a corona discharger in that corona production (e.g., ozone nitride) is not produced.
However, toner and paper dust are attracted to the surface of the transfer roller which has a conductive and elastic outer layer. The surface of the transfer roller must be designed to facilitate the removal of toner and paper dust to permit repeated use over a long period of time. Thus, the transfer roller is required to have a smooth surface with a low frictional resistance for facilitating its cleaning by a cleaning member. However, since the transfer roller's outer layer has a rough surface with a high frictional resistance, toner and paper dust will be strongly attracted to the conductive and elastic outer layer. Thus, in conventional image forming apparatuses, users are forced to frequently replace the transfer rollers to obtain a high quality image.
In another prior art embodiment, a transfer roller includes an outer layer formed of a material having a lower coefficient of friction. While it is easy to clean the surface of such a transfer roller, its lower frictional resistance will not effectively pull the recording medium between the transfer member and the image bearing member.